1. Field of the Invention
The present invention relates to a piston assembly which finds particular but non-limiting application as a valve actuator.
2. Description of the Prior Art
In known piston assemblies a piston is caused to slide within a chamber by the supply of a pressurised operating fluid, on one side of the piston. Difficulties arise in dealing with the operating fluid upon the return stroke of the piston. The return stroke is often effected by means separate from the operating fluid. A feature often found in known arrangements is volume compensation. That is, operating fluid is provided on both sides of the piston and reciprocation of the piston within the chamber requires compensation, for the resulting change in volume occupied by the operating fluid on either side of the piston. Providing such a feature is relatively burdensome in the design and manufacture of the arrangement.